Thermal Management


Although thermal management is important in internal combustion engine vehicles, Lithium Ion cell temperature management is of vital importance in an electric vehicle, both for the safety and battery longevity.

The thermal management system controls three functions:

  • The temperature, humidity and flow volume of the air in the cabin

  • The battery temperature

  • The temperatures of the powertrain and high voltage electronic systems

These three functions are achieved by using three subsystems:

These three systems are interconnected and share many key components. Each can operate independently or together, depending on thermal requirements. This section contains information on all components that comprise these three subsystems.

Controls for the cabin HVAC system are accessed in the normal way, conversion being done between the Rolls Royce panel and appropriate CAN bus messages by the Vehicle Controller. The battery and powertrain systems are autonomous and cannot be overridden.


Component Location

1. Sub-cool condenser fan 2. Condenser fan control module RH (LH symmetrical) 3. Battery coolant pump 14. Coolant heater 5. Particulate filter 6. Cabin HVAC unit 7. RLSH sensor 8. Rear air exhausters 9. In-car temperature sensor 10. Coolant reservoir 11. Powertrain coolant pump 12. Battery rapid mate connector 13. Four–way diverter valve14. Electric A/C compressor15. Gas-cool condenser fan16. Gas-cool condenser17. Battery coolant pump 218 Battery coolant chiller19. Ambient temperature sensor20. Coolant radiator21. Sub-cool condenser22. Receiver dryer (inside sub-cool condenser)

Component Schematic

1. Coolant radiator2. Condenser/drier and fan3. Battery coolant chiller4. Compressor5. DC-DC converter6. HVAC blower motor7. Evaporator8. PTC heater9. Battery coolant heater10. Battery11. Drive inverter12. Gearbox13.Motor stator14. Motor rotor15. Onboard slave charger16. Onboard master charger17. Coolant reservoir

Thermal Controller (THC)

The THC is an enclosed printed circuit board (PCB) mounted on the HVAC unit.

The THC receives the following direct inputs:

  • Coolant temperature

  • Refrigerant pressure and temperature

  • Coolant level

The THC controls the following outputs:

  • A/C compressor

  • TXV solenoids

  • Condenser fan controllers

  • Coolant pumps

  • Coolant diverter valves

  • Active louvers (radiator/condenser air flow control)

  • PTC heater demand

  • Coolant heater demand

The THC receives feedback from the following components:

  • A/C compressor – energy consumption, faults

  • Coolant heater – temperature

  • Coolant pumps – speed, faults

  • Coolant diverter valves - position

The THC pulls the following data from the CAN network:

  • Vehicle speed

  • Charge status

  • Drive unit temperatures

  • Battery temperatures

  • Charger temperatures

  • PTC heater – temperature, duty cycle feedback, faults

  • RCCM - HVAC requests, ambient and duct temperatures, door actuator voltages, faults

From this information, the THC provides the appropriate responses to control these devices, as well as prioritizing compressor demand between the needs of the in-car evaporator and the needs of the battery coolant chiller.

The THC also receives and interprets diagnostic information and fault codes. This information is reported to the gateway controller via the powertrain CAN bus for communication to technicians.

Cabin HVAC

Cabin Air Distribution

The cabin HVAC system controls the temperature, humidity, flow volume, distribution, and quality of air within the car to achieve and maintain the conditions requested by the driver.

One of the features of the air conditioning system is that all air entering the system is dehumidified and cooled. This is done by passing the air through the refrigeration evaporator matrix before it enters the heater and HVAC unit.

The upper and lower systems operate independently, each system having its own air temperature sensor chain, temperature selector, servo mechanism. blend flap and electronic circuitry. The heater and control box supplies hot and cold air to the two independent ducting systems. The upper system delivers air to the windscreen demister outlets, circular facia outlets and the rectangular facia outlet. The lower system delivers air to the tower outlets in both the front and rear compartments of the car.

Air enters the vehicle through openings at the base of the windshield. It passes through the particulate filter and is drawn into the HVAC unit by two fans controlled by the blower motor control module. The air is then forced into the HVAC unit through an expansion duct to the evaporator. The evaporator cools and dehumidifies the air and transfers it to the Positive Temperature Coefficient (PTC) heater.

After cooling and dehumidifying as necessary, the air passes to a split temperature blend door operated by two actuators, the position of which determines the ratio of hot and cold air required to achieve the preselected temperatures. The actuators are controlled by the Remote Climate Control Module (RCCM). This diverts air through or around the cabin heater depending on the temperature of air required at the outlet ducts. A set of air distribution doors in the HVAC unit directs the conditioned air to the distribution outlets. The outlets from the HVAC unit include the window demister outlets, the circular facia outlets, the rectangular facia outlets. Each front outlet has temperature sensors to provide feedback for temperature control.

The temperature blend doors are located between the evaporator and the PTC heater. The single PTC heater core cannot match the performance of an internal combustion engine’s dual zone air temperature control, due to the possibility of overheating the single PTC heater.

The air conditioning system also includes a coolant tap mechanically operated (in conjunction with the lower servo mechanism), two air recirculation flaps, a windscreen/facia mode change flap and a lower air quantity flap. These are operated by electrical actuators upon signals related to servo positions. A rear window demister is incorporated into the system. The demister element is automatically switched on whenever the car is being heated, this being the only time that misting or ice formation is likely to occur.

Recirculation and Outside Air Controls

The recirculation and outside air modes allow air to be drawn into the cabin HVAC unit from inside the car in recirculation mode, or from outside the car. The driver can select recirculation mode to avoid traffic fumes being drawn in from outside. Recirculation also maximizes heating and cooling by using conditioned recirculated air. Various automatic control modes adjust the percentage of recirculated and outside air to give the most efficient operation while providing optimum comfort and humidity control. The recirculation logic is tuned for front passenger comfort only, since this logic provides the most efficient HVAC operation.

Outside air mode can be used to provide more second row comfort as air is pulled into the cabin from the HVAC unit and is exhausted via the rear air exhausters. If windows begin to fog, select outside air mode. If outside air mode is not sufficient to reduce fogging, select defrost mode.

Remote Climate Control Module (RCCM)

The RCCM is an enclosed Printed Circuit Board (PCB) that is mounted on the HVAC unit and receives signals from the following sensors:

  • Ambient air temperature

  • In-car air temperature

  • Evaporator temperature

  • Front air duct discharge temperature

The RCCM communicates on the fault-tolerant body CAN bus. It broadcasts data from these inputs to the Thermal Controller (THC). The RCCM calculates a requested A/C compressor speed based on the evaporator actual temperature versus the target temperature. The thermal controller receives this request and directly commands the compressor as needed. The thermal controller might override the RCCM request in the case of power limiting or high chiller load.

The RCCM has direct control over the blower motor and the mode/blend door actuators.

Positive Temperature Coefficient (PTC) Heater

The PTC heater is a high voltage heating device using ceramic heating stones as resistors. The electrical resistance of the stones increases as their temperature rises. This provides a safety mechanism to prevent overheating. The heater consists of a heating matrix including the heating stones, a conductive plate, and aluminum fins. The controller is mounted in a housing connected to the matrix and supplies the high voltage power to the heating stones. The controller uses six sets of Insulated Gate Bipolar Transistor (IGBT) circuits to switch the DC power, and a pulse width modulation circuit that provides variable power to regulate the amount of heat generated.

The PTC heater is on the body fault-tolerant (BFT) CAN bus. The RCCM requests a PTC duty cycle to the Thermal Controller and the THC sends the final command to the PTC heater. In certain conditions, the Thermal Controller overrides the RCCM request in the case of low HV power available, range drive mode, and end of charge taper for the HV battery.

The PTC heater uses four internal temperature sensors for internal temperature limiting. Two sensors are on the heating grid, and two more are located on the drive IGBTs. If any of these sensors faults, the PTC does not operate. The PTC also does not operate if it does not receive correct signals from the RCCM's discharge air temperature sensors over the CAN bus.

High voltage is supplied directly from the DCDC converter. The PTC heater HV fuse is also located internally to the DCDC converter.


  1. Defrost air temperature sensor

  2. Driver discharge air duct temperature sensor

  3. Evaporator temperature sensor

  4. Driver floor air temperature sensor

  5. In-car temperature sensor

  6. Passenger discharge air duct temperature sensor

  7. Passenger floor air temperature sensor

  8. Blower motor control module

  9. Coolant reservoir low coolant level sensor

  10. Battery inlet temperature sensor

  11. Ambient air temperature sensor

Ambient Air Temperature Sensor

Located next to the coolant radiator, this is a negative temperature coefficient (NTC) sensor. This sensor is directly connected to the RCCM, which broadcasts both raw and averaged ambient temperature to the THC. The averaged temperature is displayed on the touchscreen for driver information.

In-Car Temperature Sensor

Located behind the instrument cluster, this is a negative temperature coefficient (NTC) sensor. This sensor supplies the RCCM and in turn the THC with a signal representing the temperature inside the car.

Discharge Air Duct Temperature Sensor

These sensors monitor the temperature of air flowing through the driver and passenger discharge air ducts, providing feedback to the RCCM. The discharge air temperature actual is compared to the calculated discharge temperature target, which the RCCM uses to adjust the PTC heater duty cycle and the temperature blend doors. This maintains the desired air temperature for both front seat occupants.

Rain/Light/Solar/Humidity (RLSH) Sensor

courtesy Tesla motors
  1. Rain/Light/Solar/Humidity (RLSH) Sensor

The rain/light/solar/humidity (RLSH) sensor is located on the windshield, in a housing directly in front of the rear view mirror. It requires some airflow to function correctly, provided by holes in the housing. It is connected to the body controller via a LIN communication circuit. The body controller broadcasts data from the RLSH sensor on the body CAN bus to the Gateway, which then puts the data on the fault-tolerant body CAN bus for use by the RCCM.

The RCCM uses solar load information to estimate the heating effect on the vehicle from sunlight. It uses this input to maintain the desired cabin temperature as the solar load varies.

The RCCM also measures windshield temperature and in-car humidity. If conditions for windshield fogging are detected, the RCCM attempts to reduce fogging by forcing fresh air, turning on partial defrost mode, and turning on the evaporator. If the vehicle is in a severe fogging condition, the driver might still need to select a defrost mode to provide maximum visibility.

Evaporator Temperature Sensor

The evaporator temperature sensor is an NTC sensor that extends into the airflow on the outlet side of the evaporator. It provides the RCCM with a temperature signal, which the RCCM uses to control the requested RPM of the A/C compressor, and thus the operating temperature of the evaporator. The RCCM supplies the evaporator temperature sensor with a 5V reference voltage and translates the return signal voltage into a temperature. If the sensor develops a fault, the RCCM adopts a default temperature of 0°C (32°F).

Blower Motor Control Module

The HVAC blower motor speed request is sent from the RCCM as a Pulse Width Modulation (PWM) signal to the blower motor control module. The switching frequency of the module's MOSFET driver determines the voltage supplied to the blower motor, and therefore blower motor speed.

Particulate Filter and Filter Housing

The particulate filter prevents dust and pollen from entering the cabin through the HVAC system. This serviceable filter is located in the housing previously used to filter air for the combustion engine, located on the front right hand side of the engine compartment.

Refrigeration System


Showing Condenser, Receiver/Drier and Condenser Fan(s)

The A/C system extracts heat from inside the car and transfers it to the outside atmosphere.

The refrigerant is circulated by a compressor which pumps high pressure vapour to the condenser matrix where it condenses from vapour at the top of the matrix to a liquid at the bottom of the matrix. The liquid passes to a receiver/drier which absorbs any traces of moisture that may be present and it also ensures that the refrigerant passes to the expansion valve in liquid form.

The refrigerant lines contain high pressure and low pressure charge ports, and high and low side refrigerant pressure and temperature sensors.

A sight glass on the drier enables the refrigerant to be inspected whilst the system is operating when a steady flow of liquid should be observed. if bubbles or foam can be seen it usually indicates incorrect operation of the system or insufficient refrigerant. However it is normal for some foaming to show when the ambient air temperature is below 21 'C. The refrigerant is pumped to the Thermal Expansion Valve (TXV) which controls the flow of refrigerant to the evaporator. To achieve this, the temperature and pressure is sensed.

In addition to providing conditioned air inside the car, the A/C system uses additional refrigerant lines to direct condensed refrigerant to a second TXV and battery coolant chiller assembly. This system controls the temperature of the battery and the powertrain components.

Electronic solenoid valves integral to the TXVs shut off refrigerant flow to either the car evaporator or battery coolant chiller when either of those systems is not in use. The refrigerant system is a sealed, closed-loop system filled with a refrigerant charge of either R-134a (US Specification vehicles) or HFO-R1234yf (European specification vehicles) refrigerant as the heat transfer medium.

A non-conductive Polyolefin Ester refrigerant oil is added to the refrigerant to lubricate the internal components of the compressor. This is supplied in the compressor during manufacture. Whenever the system is discharged and/or components are replaced, refrigerant and oil must be replaced in an equivalent weight to what was removed.

NOTE: The A/C system contains 770 +/- 20g (1.7 lb +/- 0.044 lb) of refrigerant and 150 grams (0.33 lb) of ND-11 refrigerant oil.

Refrigerant Cycle

  1. Sub-cool condenser and fan

  2. Gas-cool condenser and fan

  3. Compressor

  4. Battery coolant chiller

  5. HVAC blower motor

  6. Evaporator

  7. PTC heater

The electric A/C compressor pumps refrigerant through the system. It receives the low pressure, low temperature gas from the evaporator and/or battery coolant chiller. The gas is compressed into high pressure, high temperature vapor by the compressor. This high pressure, high temperature vapor enters the gas-cool condenser and fan assembly, which cools the vapor by releasing the refrigerant heat to the ambient air. The cooler vapor transfers to the sub-cool condenser, where it condenses into liquid refrigerant. As the liquid passes through a mesh filter and into the receiver/dryer inside the sub-cool condenser, any moisture in the refrigerant liquid is removed by the desiccant granules. If this moisture is not removed, it can freeze and prevent normal A/C operation.

The liquid refrigerant is then transferred to one or both of the TXVs that regulate the flow of liquid refrigerant into the evaporator or battery coolant chiller. It also reduces its pressure by expanding the high pressure cool liquid to a low pressure atomized spray. Liquid refrigerant spray enters the evaporator and the battery coolant chiller, where it absorbs heat from the surrounding area, causing the refrigerant to boil and then vaporize. This produces the cooling effect inside the car. Finally the vaporized refrigerant is drawn back into the compressor and pressurized again. This repetitive cycle continues while the A/C system is operating.


courtesy Tesla motors

  1. Low pressure inlet

  2. Mounting bracket

  3. Isolators

  4. A/C compressor

  5. High pressure outlet

  6. High voltage connector

  7. 12 volt connector

The compressor is in the space previously occupied by the automatic transmission unit. It is a high voltage (HV) electric Direct Current (DC) scroll type pump with a maximum rotational speed of 8600 RPM.

The compressor has two connectors, one for low voltage and one for high voltage. Communication with the THC is via PWM. The low voltage connector is a six-pin connector. The signals/wires used are 12V Power, Ground, Compressor Enable, Fault Response, kW Response, and Speed Request.

The compressor operates in any normal range of HV battery SOC. The compressor inverter converts the PWM request from the THC into a motor drive speed. The compressor's internal 12V power supply is generated from the HV input. The low voltage harness connections to the vehicle are used for communication only. If HV is not present at the compressor, there is no communication response.

High voltage is supplied directly from the DCDC converter. The compressor HV fuse is also located internally to the DCDC converter.

The High Voltage InterLock (HVIL) is fitted to the DCDC converter connector. The compressor side of the HV cable does not contain a HVIL circuit, so it is important not to disconnect the cable from the compressor unless the cable has first been disconnected from the DCDC converter.

WARNING: Always disconnect the compressor HV harness at the DCDC converter before disconnecting the HV harness from the compressor.

NOTE: The compressor contains non-conductive Polyolefin Ester lubricating oil. The compressor must be kept upright at all times to retain this oil in the sump.

ND-11 refrigerant oil is the only approved compressor oil for Model S. Any oil not designated ND-11 voids the compressor warranty and potentially causes HV isolation issues.

CAUTION: Use of an incorrect oil might affect the dielectric strength of the motor and cause an internal short circuit, as well as affecting bearing life.

CAUTION: Never leave the refrigerant lines or compressor unsealed. This creates a risk of water accumulating in the A/C system. The water might then freeze and restrict the flow of refrigerant around the system.


The condenser is mounted at the front of the vehicle behind the coolant radiator. It is connected to the standard Rolls Royce receiver drier.

During normal driving, the condenser dissipates heat from the refrigerant to the air being forced through it. Air is forced through the condenser either by the movement of the vehicle or by operation of the condenser fans.

Condenser Fans

If refrigerant cooling is requested when the vehicle is stationary or traveling at low speeds, the fans mounted on the condenser are activated to increase the air flow through the condenser. This increases the dissipation of heat from the refrigerant.

Condenser Fans Control Module

courtesy Tesla motors
  1. Condenser fan control module

Each condenser fan has its own fan control module mounted to the outer surface of the front body rail near the fan. The condenser fan control module is controlled via a Pulse Width Modulation (PWM) signal from the Thermal Controller (THC).

Receiver Dryer

The standard Rolls Royce receiver dryer is used. Its main function is to remove moisture and contaminants from the refrigerant, but it also acts as a temporary storage area for the refrigerant. It provides a reservoir of liquid refrigerant to accommodate changes in heat load at the evaporator. The refrigerant is then passed to either the TXV on the evaporator or the one on the battery coolant chiller.

Without the receiver dryer, any moisture in the system might form ice in the TXV, restricting the flow of refrigerant in the system.

Refrigerant Temperature and Pressure Transducers

A refrigerant temperature and pressure transducer, located on the low pressure line leading to the compressor, measures the temperature and pressure of the refrigerant on the low pressure side of the system. A high pressure side refrigerant temperature and pressure transducer is located in the high pressure line between the compressor and gas-cool condenser, and measures the temperature and pressure of the refrigerant on the high pressure side of the system.

The refrigerant temperature and pressure transducers are used to provide system response to control compressor and condenser fan speed. The suction and discharge sensors use the same electrical connector and mechanical interface to the A/C line. Despite these mechanical similarities, their internal calibrations are different and are therefore NOT interchangeable.

WARNING: There are no Schrader valves under the transducers. Refrigerant must be recovered from the system before removing any transducer.

Thermal Expansion Valves (TXV)

Two TXVs are fitted in the system. One is fitted to the refrigerant inlet and outlet of the HVAC evaporator and the other to the refrigerant inlet and outlet of the battery coolant chiller. Each TXV has a solenoid valve and a moving valve needle. The solenoid valve opens when the system is operating and shuts when it is switched off. The moving needle creates a variable orifice in the valve to control the flow of refrigerant into the evaporator or the battery coolant chiller when the system is operating.

The solenoid valves on both TXVs must be open when charging the A/C system.

The needle valve is operated by the difference in temperature at the refrigerant outlet and inlet. The needle valve also uses a tuneable spring at the bottom of the valve housing. The valve needle is attached to the charge cylinder at the top of the valve housing, which responds to the refrigerant outlet temperature. The valve is closed at low outlet temperatures but opens at high outlet temperatures to allow more refrigerant into the evaporator or battery coolant chiller. The spring is set to ensure that all liquid refrigerant vaporizes before entering the evaporator or battery coolant chiller. The needle valve regulates the quantity of refrigerant flow into the evaporator or battery coolant chiller in accordance with the heat transfer required by air passing through the evaporator fins or coolant passing through the battery coolant chiller.


The evaporator is integral with the HVAC unit located under the dash. It cannot be removed independently of the HVAC unit.

High pressure, low temperature refrigerant changes from liquid to vapor as it enters the evaporator, and absorbs large quantities of heat as it changes state. As the air passing through the evaporator cools, moisture in the air condenses on the evaporator surface, drying the air that is delivered to the interior of the car.

Excess moisture collects in the bottom of the HVAC unit and is drained through a hose routed through the dash panel.

The inlet and outlet pipes of the evaporator are routed through the dash panel, providing a fixing point for the evaporator TXV. A foam seal surrounding the TXV provides an air and water seal at the opening in the dash panel.

Evaporator Outlet Temperature Sensor

A temperature sensor at the evaporator outlet provides feedback to the Remote Climate Control Module (RCCM) on the amount of cooling taking place within the evaporator. The RCCM uses this input to determine the compressor RPM request that it sends to the THC.

Refrigerant Lines

Aluminum and rubber refrigerant line assemblies connect the system components together. O-rings are fitted between the connections to ensure a secure seal. To maintain similar rate of flow around the system, the diameter of the refrigerant lines varies to suit the two pressure and temperature sections. The larger diameter hoses are used on the low pressure/low temperature section and smaller diameter pipes are used on the high pressure/high temperature section.

Service Ports

The high and low pressure service ports are located under the hood and are an integral part of the refrigerant lines. The high pressure port is on the line between the sub-cool condenser outlet and evaporator inlet. The low pressure charge port is on the line between the evaporator outlet and the compressor inlet.

Schrader valves form the ports in the refrigerant lines and allow connection of charging/evacuation equipment for servicing purposes. The connections are standard couplers for R134a or R1234yf. The valves are fitted with a screw-on cap to prevent refrigerant leaking through the valves and to prevent dirt from entering. Each refrigerant type requires a unique port size and associated coupler.

WARNING: Servicing must only be carried out by personnel familiar with both the vehicle system and the charging and testing equipment. All operations must be carried out in a well-ventilated area away from open flame and heat sources.

WARNING: HFO-R1234yf and R134a are considered hazardous liquids and can cause serious injury if handled incorrectly. Suitable protective clothing, consisting of face and eye protection, heat-proof gloves, rubber boots, and apron or waterproof overalls must be worn when carrying out operations on the air conditioning system.

CAUTION: Keep the charge ports capped at all times to prevent contamination.

CAUTION: Use Toolbox to initiate the HVAC service mode before beginning evacuation and recharge procedures. The thermal controller Refrigerant Fill command opens both TXV solenoids to assist with evacuating and filling the refrigerant system.

NOTE: Always locate and repair the source of a refrigerant leak before recharging the system

Battery and Powertrain Cooling/Heating

1. Coolant radiator 2. Radiator bypass valve 3. Battery coolant pump 1 4. Coolant chiller 5. Coolant heater 6. Powertrain coolant pump 7. Coolant pipe 8. Coolant reservoir 9. Series/parallel diverter valve 10. Coolant chiller bypass valve 11. Battery coolant pump 2

The heating and cooling system includes a radiator, hoses, coolant pumps, and valves arranged to provide heating and cooling to the powertrain components and the high voltage Battery. The coolant can circulate in two modes: series mode and parallel mode. Series mode configures the cooling system so that the Battery and powertrain are heated or cooled in series, with heat transfer occurring between the two subsystems. In parallel mode, the Battery and powertrain loops run decoupled from each other and do not appreciably transfer heat between the two systems.

The dual function system incorporates a four-way coolant diverter valve with two inlets and two outlets that can switch coolant routing.

Heating and Cooling Modes

The following modes are available for powertrain heating and cooling requirements. The system automatically implements the most appropriate mode according to the prevailing conditions.

Series Mode - Battery Heating

During cold soak conditions, series mode allows coolant to flow through the motor to heat coolant, bypass the radiator and then flow into the HV Battery for warming the Battery cells. If additional heating is required, the high voltage coolant heater can be activated to provide additional heat to the coolant just prior to entering the Battery.

Series Mode - Reduced Cooling Energy

Series mode is also an effective configuration when used in low ambient temperatures. This allows cooling of the Battery and powertrain using only the radiator, without the need for operating the A/C compressor and chiller system for Battery cooling.

Series Mode - High Ambient Powertrain Cooling

In extremely hot conditions when the radiator cooling of the powertrain is limited, the Battery can act as a thermal capacitor to absorb powertrain heat and allow the motor to run cooler. This improves motor efficiency. It is only effective until the Battery temperature reaches its thermal limits. To extend high temperature operation, the chiller and A/C compressor can be engaged to chill coolant going to the Battery and subsequently the powertrain components.

Parallel Mode

Parallel mode allows the most efficient use of the radiator for powertrain cooling, because the powertrain coolant can run at much higher temperatures than the Battery coolant. This mode also allows the Battery to heat itself gradually so that it does not require active cooling, even if it absorbed significant amounts of powertrain waste heat.

Also, if the Battery requires cooling but the powertrain does not, the Battery coolant chiller system can be activated solely to cool the Battery. During charging, the charger(s) are cooled on the powertrain cooling loop. Operating in parallel mode allows this to happen without adding heat to the Battery.

Series/Parallel Diverter Valve

The series/parallel mode valve is a 4-way valve that is controlled by the THC. It contains a position sensor that the THC monitors for comparing desired valve position to actual. It is used to switch the coolant flow path from going through the Battery and powertrain in series, to diverting the coolant flow path into two parallel loops. The Battery loop consists of the HV Battery, DCDC converter, chiller, and coolant heater. The powertrain loop consists of the chargers, the drive unit, the radiator, and the coolant reservoir.

The THC can select two paths for coolant flow through the system. In series mode, coolant flows through the Battery and powertrain in a continuous loop. If the temperature of the Battery is below nominal, heat from the powertrain can be used to passively raise the temperature of the Battery. The major advantage of this strategy is that it does not require additional energy to actively heat the Battery using the coolant heater. If the temperature of the Battery must be managed independently, the THC commands the valve to the parallel mode position. In parallel mode, the Battery is isolated from the powertrain coolant loop, and can be actively cooled without being affected by powertrain temperature fluctuations.

Coolant Bypass Valves

courtesy Tesla motors
  1. Bypass valve

The thermal management system has two coolant bypass valves: one for the radiator and one for the chiller. The two valves are interchangeable. They are directly controlled by the THC, and have position sensors that the THC monitors for comparing each desired valve position to the actual position.

The radiator bypass valve is mounted to the right front outboard corner of the subframe. The THC commands the valve to the full radiator position if the system is in parallel mode, or if it is in series mode and either:

  • The Battery inlet temperature is greater than the Battery active cooling target

  • The powertrain inlet temperature is greater than the powertrain active cooling target

The THC commands the valve to the full bypass position when:

  • The Battery heater is commanded on

  • The Battery AND powertrain passive cooling target is 10C greater than the inlet temperature

The chiller bypass valve is mounted on the left side of the subframe, behind the ABS modulator. The THC commands the valve to the full chiller position if there is a request for A/C compressor operation to cool the Battery. Otherwise, the chiller is bypassed. The bypass valve slowly introduces coolant to the battery coolant chiller, so that the TXV does not open fully and starve the HVAC evaporator of refrigerant. Such starvation would result in large variations in the air temperature from the HVAC vents when the chiller is engaged.

Coolant Heater

courtesy Tesla motors
  1. Coolant heater

  2. Coolant inlet

  3. Coolant outlet

  4. Temperature sensor connector

The coolant heater is located under the hood, on the right-hand side near the bulkhead. The purpose of the coolant heater is to heat the battery coolant to a minimum temperature for Battery charging. The coolant heater is controlled by the DCDC converter controller, which switches the heater on or off as necessary.

The coolant heater has a sensor that monitors its internal temperature and reports this information to the THC to prevent overheating.

High voltage is supplied directly from the DCDC converter. The coolant heater HV fuse is also located internally to the DCDC converter.

Coolant Reservoir Assembly

Tesla 'SuperBottle'

  1. Coolant reservoir

  2. Coolant pump 1

  3. Coolant pump 2

  4. Coolant chiller

  5. 4-way valve

To simplify plumbing and save space, TeslaRR uses the Model 3 'Superbottle', which packages two pumps, one heat exchanger, a coolant control valve and a coolant level sensor, all within the bottle itself.

The coolant reservoir maintains a reserve of 2 liters of coolant and 1 liter for expansion and contraction of the coolant level. It is mounted in the same position as the original Rolls Royce radiator header tank . The reservoir is a flow-through de-gas bottle: the majority of the coolant flows past the bottle, while a small portion of the coolant stream flows into the bottle. The coolant that does flow into the bottle passes through a series of settling chambers that allows air to migrate out of the coolant within several minutes. Air-free coolant is then drawn from the reservoir. The coolant level is reported to the THC, and should be between the Nominal and Maximum lines when the vehicle is at ambient temperature.

The coolant chiller is a refrigerant-to-coolant heat exchanger part of the 'Superbottle'. The coolant chiller is used for active cooling of the Battery and DCDC converter. It can also support cooling of the drive unit (motor, gearbox and inverter) and power electronics.

The coolant chiller is fitted with a TXV on the inlet and outlet ports and is serviced as an assembly.

Coolant Pumps

TeslaRR has three coolant pumps: two battery coolant pumps and one powertrain coolant pump.

The two battery coolant pumps are identical brushless 12V DC centrifugal pumps. Controlled by the THC, they pump coolant around the battery to maintain it at optimum temperature.

The powertrain coolant pump is identical to the battery coolant pumps. It is located to the rear of the coolant reservoir. The powertrain coolant pump is controlled by the THC, and pumps coolant around the powertrain components to maintain them at optimum temperature.

Coolant (Glycol) Temperature Sensor

There are two coolant temperature sensors. One is in-line between the coolant heater and the Battery, and provides the Battery inlet coolant temperature to the THC. The other is in-line between the powertrain pump and the charger(s), and provides powertrain inlet coolant temperature to the THC. The Battery, charger(s), and drive unit report internal temperatures to the THC, which then adjusts coolant flow rate, path, and temperature accordingly to keep those components within their nominal operating range.


The coolant used is G-48 coolant, supplied pre-mixed with water in the proper concentration. G-48 is a long-life coolant designed for high aluminium content powertrain systems.

CAUTION: Do not top off or refill the cooling system with any other type of coolant.